Cross-Linked PEG Membranes of Interpenetrating Networks with Ionic Liquids as Additives for Enhanced CO2 Separation

Polyethylene glycol (PEG)-based membranes have recently been reported with excellent CO2 separation performances. However, the commonly exhibited high crystallinity may deteriorate the gas permeation properties in this type of membrane. In this work, a two-stage cross-linking method was employed to fabricate PEG membranes with interpenetrating networks to reduce the crystallinity. Ionic liquids (ILs) were incorporated into the resultant membranes to further increase CO2 diffusivity and the CO2 affinity of the membranes. By increasing the length of the PEG-based acrylate monomers and optimizing the ratio of the amine-functionalized cross-linker to the acrylate monomers, we significantly enhanced the CO2 permeability of the resultant membranes (from 0.6 to 85.0 Barrer) with slightly increased CO2/N2 selectivity. Four conventional ILs (i.e., [Bmim][BF4], [Bmim][PF6], [Bmim][NTf2] and [Bmim][TCM]) with different anions were added into the optimized cross-linked PEG membranes. The addition of ILs endows superior gas transport properties at high loadings, and the [Bmim][TCM] gives the best CO2 separation performance of the membranes; CO2 permeability of up to 134.2 Barrer with the CO2/N2 selectivity of 49.5 was documented. The anions in ILs were found contributing the most in promoting the CO2 permeation, and the higher CO2 affinity endows the better CO2 separation performance in the resultant membranes.